add bytes api benchmark.

@@ -756,6 +756,17 @@ About the HLS overhead of SRS, we compare the overhead to FLV by remux the HLS t
 
 The HLS overhead is calc by: (HLS - FLV) / FLV * 100%
 
+### Bytes Api
+
+The api provides bytes of vhost, stream and srs.
+
+| Connections | tcpdump     | srs         |  deviation |
+|      1      | 201687968   | 201687968   |   0%       |
+|     100     | 12456042662 | 12458284053 |   0.018%   |
+|     500     | 11623083989 | 11633158616 |   0.087%   |
+
+The tcpdump command is `tcpdump src 192.168.1.151 and port 1935 -i eth0 and tcp -ql`.
+
 ## Architecture
 
 SRS always use the most simple architecture to support complex transaction.